Preparation of carbon disulfide



Patented Aug. 21, 1951 2,565,215 PREPARATION OF CARBON DISULFIDE Hillis0. Folkins and Elmer L. Miller, Skokie, 111., assignors to The Pure OilCompany, Chicago, 111., a corporationof Ohio No Drawing. ApplicationApril 25, 1947, Serial No. 744,020

27 Claims. 1

This invention relates to a method of producing carbon disulfide.

This application is a continuation-in-part of our application SerialNumber 576,699, filed February 7, 1945, now abandoned.

In United States Patent 2,330,934, of October 5, 194.3, to Thacker, andassigned to The Pure Oil Company, there is disclosed a method ofpreparing carbon disulfide by reacting hydrocarbons such as methane withsulfur at temperatures of approximately 450 to 700 C. in the presence ofa catalyst such as silica gel, fullers earth, bauxite or activatedalumina.

We have discovered that high yields of carbon disulfide can be obtainedby reacting hydrocarbons and sulfur in the presence of syntheticsilica-alumina catalysts under the conditions set forth in the aforesaidpatent. We have further discovered that the activity of silica-aluminacatalysts in the catalysis of the reaction between hydrocarbons andsulfur to form carbon disulfide reaches a maximum when the silicacontent of the catalyst is approximately 2 to 10 er cent by weight ofthe catalyst. Synthetic silica-alumina catalysts containingapproximately 2 to 10 per cent by weight of silica are more active overthe entire temperature range than activated alumina substantially freeof silica and are more active than silica gel at temperatures aboveapproximately 575 C.

An object of our invention is to provide an improved method forproducing carbon disulfide.

Another object of our invention is to provide a catalyst capable ofgiving high yields of carbon disulfide from sulfur and hydrocarbons.

Other objects of our invention will be apparent from the followingdescription.

In accordance with our invention, sulfur and hydrocarbons, such asmethane, ethane, propane. butane or any mixture thereof and mixtures ofthe aforesaid hydrocarbons with olefinic hydrocarbon gases such asethylene, propylene and butylene, are lore-heated to a temperatureapproximating desired reaction temperature, or somewhat higher, whichmay be between 450 to 700 C. and preferably from approximately 500 to700 C. The hydrocarbon and sulfur may be separately pre-heated and thenmixed. The heated mixture of hydrocarbon and sulfur is charged to areaction zone containing synthetic silica-alumina catalyst in granular.pelleted or other comminuted form. Catalysts useful in accordance withour invention maybe made by coprecipitation of silica and alumina fromaqueous solutions of silicon and aluminum compounds.

Methods of preparing co-precipitated synthetic silica-alumina are setforth in United States Patents 2,283,172 and 2,283,173 of May 19, 1942,to Bates. Instead of co-precipitating the silica and alumina, thealumina may be precipitated on the silica in accordance with the methodsset forth in United States Patent 2,270,090, of J anuary 13, 1942, toThomas, United States Patent 2,325,706, of August 3, 1943, to Phillip,and United States Patent 2,326,523,, f August 10, 1943, to Connolly. Weprefer synthetic silica-alumina catalysts which are substantially freefrom alkali metal action.

Typical of the synthetic alumina catalysts suitable for use in theprocess conducted according to the instant invention, are catalystsbased on such materials as Alorco, a prepared activated aluminacatalyst. The base material can be prepared according to the methoddescribed in United States Patent 2,390,272, of December 4, 1945, toRiesmeyer and Stowe, which method involves the acidification with aceticacid of a specially prepared sodium aluminate solution to precipitategelatinous aluminum hydroxide. Drying of the hydroxide thus preparedcauses dehydration and results in. the development of active materials.Silica can be deposited on the oxide by impregnating it with a givenamount of ethyl silicate and subsequently hydrolyzing the material withwater. In analogous fashion, silica can also be deposited on thealuminum oxide base by hydrolysis of sodium silicate. The catalystcontaining desired proportions of silica and alumina can be preparedfrom a solution containing a hydrolyzable silicon compound and analuminate by acidifying to form a gelatinous precipitate consisting ofaluminum hydroxide and sil'icic acid. Heating will dry out the materialsand develop the oxides in useful form.

Other methods for" preparing these catalysts may be employed. In one ofthese methods, the alumina base may be'formed by the hydrolytic actionof water on amalgamated aluminum in the presence of an organic acid,such as acetic acid. The hydrosol may be'coagulated by evaporation or bythe addition of ammonia or other suitable electrolyte. Methods ofpreparing such catalysts are set forth in United States Patent2,345,600, of April 4, 1944, to Llewellyn Heard et. al., United StatesPatent 2,369,734, of February 20, 1945, to Llewellyn Heard, and UnitedStates Patent 2,371,237, of March 13, 1945, to Llewellyn Heard et. al.The silica may be incorporated into the catalyst at one of the variousstages of the preparation by one of the methods described above. Thus,the silica and alumina may be cogelled or the silica may be added byimpregnation of the alumina gel before or after it has been washed anddried.

Our process may be carried out at atmospheric, super-atmospheric, orsub-atmospheric pressure. Excellent results are obtained at pressures ofatmospheric or slightly above. Contact between the catalyst andreactants may be eifected by passing the reactants through a stationarybed of granular or pelleted catalyst; by passing the reactants through amoving bed of granular or pelleted catalyst; or by intimately mixing thereactants with powdered catalyst which remains suspended in the reactionmixture during its passage through the reaction zone and is subsequentlyremoved from the reaction products by appropriate precipitating devices.Since the catalyst remains active for indefinite periods of time, thestationary bed type of process is the simplest and most economical.

The time of contact between reactants and catalyst is determined chieflyby the temperature of reaction. At temperatures approaching 700 C. spacevelocities will be high since the reaction progresses rapidly at thesetemperatures. At temperatures approaching 450 C. space velocities arepreferably lower. By space velocity is meant the total volume ofreacting gases measured at C. and 760 millimeters of mercury passingthrough a unit volume of catalyst per hour. Good results may be obtainedat space velocities of approximately l00.to 1,000, although it is to beunderstood that higher or lower space velocities may be used.

The sulfur and hydrocarbons to be reacted may be mixed in any desiredratio, although we prefer to mix the hydrocarbons and sulfur in a ratioapproximately equal to the stoichiometric ratio required to formhydrogen sulfide and carbon disulfide. In order to react thehydrocarbons as completely as possible, a small excess, of the order ofto per cent, of sulfur may be used in the reaction mixture. Excesssulfur present in the reaction products can be readily recovered bycondensation and can be recycled to the process.

The reaction may be carried out isothermally or adiabatically dependingupon the conditions of the reaction employed. The reaction product isseparated into its components by cooling to a temperature below thevaporization point of sulfur but above the boiling point of carbondisulfide under the existing pressure in order to condense any residualsulfur. Care should be exercised to prevent the sulfur from assuming aplastic state. Cooling to approximately 140 C. will maintain sulfur in amobile condition. Carbon disulfide may be separated from hydrogensulfide and unreacted hydrocarbons by absorption in oil, such askerosene or gas-oil fraction, and recovered by stripping the carbondisulfide from the absorbent oil. The carbon disulfide is then condensedand purified.

Hydrogen sulfide and hydrocarbons which are absorbed together with thecarbon disulfide may be separated from the condensed carbon disulfide bydistillation and may be recycled to the absorption process to avoid lossof carbon disulfide which may be contained therein. Recovery of carbondisulfide from the reaction products may be effected in accordance withthe method described in United States Patent 2,330,934, cited. Thecarbon disulfide may be separated from slight amounts of hydrogensulfide and other 4 impurities by fractional distillation or by chemicalmethods.

The residual gas leaving the absorber in which carbon disulfide isseparated from reaction products may be sent to a regeneration unit inwhich hydrogen sulfide is converted to sulfur by reaction with sulfurdioxide in known manner and the sulfur recovered may be recycled to thecarbon disulfide reactor. If it is desired to recycle unreactedhydrocarbons to the conversion procsee, they may be separated byscrubbing the mixture with an aqueous solution of sodium carbonate,sodium phosphate or organic absorbent capable of absorbing hydrogensulfide. Hydrogen sulfide may be regenerated from this treatment andrecovered as sulfur in the manner outlined.

In order to demonstrate the effectiveness of synthetic alumina-silicacompositions as catalysts for the preparation of carbon disulfide, aseries of runs was made in laboratory apparatus in which the reactorconsisted of a vertical piece of 25-20 chrome-nickel cylindrical steelpipe, 6% inches in length and 2 inches in outside diameter. The reactorwas well insulated and was heated by electric resistance coils. It wasequipped with a thermocouple well extending axially, the length of thereactor. The reactor had a catalyst capacity of 200 cc. The runs wereall made using methane as charging stock with a sulfur to methane ratioof 2, calculated on the basis of diatomic sulfur. Sulfur was charged toa pre-heating coil in a molten state by means of an accurate sulfur feedpump. Methane after being pre-heated to the desired reaction temperaturein a separate pre-heater, was mixed with the sulfur. The mixture enteredthe top of the reactor filled with catalyst and left the reactor at thebottom thereof. The reaction mixture was cooled to C. to condensesulfur. The carbon disulfide was thereafter condensed by passing thereaction products through a Dry Ice trap.

The results on the series of runs using different catalysts, all carriedout at a space velocity of 389 and with a sulfur (S2) to methane ratioof 2, are tabulated in the following table:

Table Per Cent Conversion SiOz, Per Cent Catalyst Weight e1 54. 6 70. 783. 4 90.3 Alorco, 11-40, R-220CL 46. 1 66. 2 83. 6 93. 2 Alorco, F-1028. l 48. 5 86. 6 Alorco, F-l 0. 33. 6 54. 3 70. 7 87.0 Nallco (U. 0.P.) Approx. 87.0. 47. 4 66.8 88. 5

ype. Bead, S. V. 117,040 Approx. 910. 40. 7 56.5 80.5

1 General chemical. 1 Socony-Vacuum.

It will be seen from the results in the table that at temperatures up to575 C. silica gel is the most active catalyst. Below 575 C., Alorcocontaining 5.9 per cent of silica, an activated alumina manufactured bythe Aluminum Ore Company, is less active than silica gel, but attemperatures of approximately 575 C. and upward, Alorco containing 5.9per cent of silica, is more active than silica gel. It is also apparentfrom the table that synthetic alumina-silica catalyst containingapproximately 5 per cent of silica is more active over the entiretemperature range than is activated alumina containing sub stantially nosilica, or silica-alumina catalyst containing larger amounts of silica.The maximum activity occurs when the silica content of the catalyst isapproximately 2 to per cent by weight.

The product from each run was analyzed for carbon disulfide, hydrogensulfide, methyl mercaptan, methyl sulfide and sulfur. In almost everycase the product contained in excess of 99 per cent of carbon disulfidewith hydrogen sulfide as the major impurity. For example, in a run madeat 525 C. with a catalyst containing approximately 5 per cent of silica,a product was obtained containing 99.44 per cent of carbon disulfide,0.53 per cent of hydrogen sulfide, 0.03 per cent of sulfur and no methylmercaptan or methyl sulfide. The hydrogen sulfide can be substantiallycompletely removed by fractional distillation.

The activity of synthetic silica-alumina catalysts increases as thesilica content increases up to approximately 5-10 per cent of silica andthen gradually decreases as the silica content is further increaseduntil the silica content of the catalyst is in the neighborhood of 85-90per cent silica. Increased activity is again apparent as the silicacontent approaches 100 per cent, as in the case of pure silica gel.

By utilizing synthetic alumina catalysts, particularly those in whichthe silica content is approximately 2 to 10 per cent by weight, carbondisulfide yields approaching very close to theoretical yields can beobtained at temperatures of 600 to 700 C.

It is claimed:

1. The method of preparing carbon disulfide comprising contactinghydrocarbon gas rich in methane and sulfur in approximately thestoichiometric ratio required for formation of hydrogen sulfide andcarbon disulfide with a synthetic silica-alumina catalyst consistingessentially of about 2 to 10 per cent by weight of silica on alumina ata temperature of approximately 575 to 700 C.

2. Method in accordance with claim 1 in which the catalyst contains notmore than approximately 6 per cent by weight of silica.

' 3. Method in accordance with claim 1 in which the catalyst containsapproximately 5 per cent by weight of silica.

4. The method of preparing carbon disulfide comprising contacting amixture of sulfur and hydrocarbon gas rich in methane at a temperatureof approximately 57 to 700 C. with a synthetic silica-alumina catalystconsisting essentially of about 2-10 percent by weight of silica and thebalance alumina.

5. Method in accordance with claim 4 in which the sulfur is present inthe mixture in an amount equivalent to about 10 to 15% in excess of thestoichiometric amount required.

6. Method in accordance with claim 5 in which the catalyst iscoprecipitated silica-alumina.

'7. Method in accordance with claim 5 in which the catalyst is aluminaimpregnated with silica.

HILLIS O. FOLKINS. ELMER L. MILLER.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,330,934 Thacker Oct. 5, 19432,369,377 Thacher Feb. 13, 194 5

1. THE METHOD OF PREPARING CARBON DISULFIDE COMPRISING CONTACTINGHYDROCARBON GAS RICH IN METHANE AND SULFUR IN APPROXIMATELY RICH INCHIOMETRIC RATIO REQUIRED FOR FORMATION OF HYDROGEN SULFIDE AND CARBONDISULFIDE WITH A SYNTHETIC SILICA-ALUMINA CATALYST CONSISTINGESSENTIALLY OF ABOUT 2 TO 10 PER CENT BY WEIGHT OF SILICA ON ALUMINA ATA TEMPERATURE OF APPROXIMATELY 575* TO 700* C.